The standard treponemal tests for syphilis in humans presently accepted by the United States Public Health Service are the fluorescent treponemal antibody-absorption (FTA-ABS) test and the microhemagglutination Treponema pallidum (MHA-Tp) test.
The FTA-ABS is a manual, indirect FA microscope technique utilizing whole Tp microorganisms which are air dried and acetone fixed on glass slides. A determination of a positive or negative result is made on the basis of the fluorescence observed by the technician. The test is routinely performed in large volume testing laboratories. However, it is avoided in smaller laboratories because in low volume it is not cost effective, and the technicians do not have the experience to make the subjective decisions between positive and negative results accurately. It is, however, the presently acknowledged standard.
The MHA-Tp test is an indirect hemagglutination test employing an ultrasonic lysate of Tp adsorbed on tannic acid treated red cells. The test is less sensitive than the FTA-ABS test, especially in early disease, and the working test reagent (Tp-red blood cells) is stable for only five days. Further, although it is easy to perform, it is difficult to read.
A test has now been developed which substantially alleviates the difficulties of the foregoing techniques. It is specific, sensitive, easy to perform, objective and quantitative.